An assembled battery device includes an assembled battery and a voltage measurement circuit. In the assembled battery, a plurality of unit batteries are connected in series. The voltage measurement circuit is connected to the unit batteries via lines and configured to monitor the unit batteries. If the lines lost continuity, the voltage measurement circuit cannot properly monitor the unit batteries. To resolve such a problem, an assembled battery device having a function for detecting discontinuity of lines is provided. The assembled battery device includes a plurality of capacitors having different capacitance and connected to the unit batteries in parallel. In this device, a variation in voltage is different in a normal condition and an abnormal condition that may be caused by the lines that has lost continuity. By detecting a difference in the voltage variation, discontinuity of the line can be detected.
The assembled battery device requires a plurality of capacitors with different capacities for detecting discontinuity of the lines. Namely, the assembled battery device has structural limitations. Therefore, a different method for detecting discontinuity of lines may be preferred.
In this specification, a new technology for detecting discontinuity of lines that connect plurality of unit cells (e.g., unit batteries) to a cell monitoring device (e.g., voltage measurement circuit).